Inhaled hydrogen sulfide improves graft function in an experimental model of lung transplantation

Abstract

Objectives: Ischemia/reperfusion injury (IRI) is a common complication of lung transplantation (LTx). Hydrogen sulfide (H(2)S) is a novel agent previously shown to slow metabolism and scavenge reactive oxygen species, potentially mitigating IRI. We hypothesized that pretreatment with inhaled H(2)S would improve graft function in an ex vivo model of LTx.

Methods: Rabbits (n = 10) were ventilated for 2 h prior to heart-lung bloc procurement. The treatment group (n = 5) inhaled room air (21% O(2)) supplemented with 150 ppm H(2)S while the control group (n = 5) inhaled room air alone. Both groups were gradually cooled to 34°C. All heart-lung blocs were then recovered and cold-stored in low-potassium dextran solution for 18 h. Following storage, the blocs were reperfused with donor rabbit blood in an ex vivo apparatus. Serial clinical parameters were assessed and serial tissue biochemistry was examined.

Results: Prior to heart-lung bloc procurement, rabbits pretreated with H(2)S exhibited similar oxygenation (P = 0.1), ventilation (P = 0.7), and heart rate (P = 0.5); however, treated rabbits exhibited consistently higher mean arterial blood pressures (P = 0.01). During reperfusion, lungs pretreated with H(2)S had better oxygenation (P < 0.01) and ventilation (P = 0.02), as well as lower pulmonary artery pressures (P < 0.01). Reactive oxygen species levels were lower in treated lungs during reperfusion (P = 0.01). Additionally, prior to reperfusion, treated lungs demonstrated more preserved mitochondrial cytochrome c oxidase activity (P = 0.01).

Conclusions: To our knowledge, this study represents the first reported therapeutic use of inhaled H(2)S in an experimental model of LTx. After prolonged ischemia, lungs pretreated with inhaled H(2)S exhibited improved graft function during reperfusion. Donor pretreatment with inhaled H(2)S represents a potentially novel adjunct to conventional preservation techniques and merits further exploration.

Figure 1

(A) Partial pressure of oxygen and (B) carbon dioxide and (C) mean pulmonary artery and (D) airway pressures over time during reperfusion. Lungs pre-treated with room air are displayed with a dashed line. Lungs pre-treated with hydrogen sulfide are displayed with a solid line. Asterisks indicate a post hoc statistical difference at given time points as determined by the Tukey-Honest significance difference test. Abbreviations: n, number; RM-ANOVA, repeated measures analysis of variance; GEE, generalized estimating equation; H2S, hydrogen sulfide.

Figure 1

(A) Partial pressure of oxygen and (B) carbon dioxide and (C) mean pulmonary artery and (D) airway pressures over time during reperfusion. Lungs pre-treated with room air are displayed with a dashed line. Lungs pre-treated with hydrogen sulfide are displayed with a solid line. Asterisks indicate a post hoc statistical difference at given time points as determined by the Tukey-Honest significance difference test. Abbreviations: n, number; RM-ANOVA, repeated measures analysis of variance; GEE, generalized estimating equation; H2S, hydrogen sulfide.

Figure 1

(A) Partial pressure of oxygen and (B) carbon dioxide and (C) mean pulmonary artery and (D) airway pressures over time during reperfusion. Lungs pre-treated with room air are displayed with a dashed line. Lungs pre-treated with hydrogen sulfide are displayed with a solid line. Asterisks indicate a post hoc statistical difference at given time points as determined by the Tukey-Honest significance difference test. Abbreviations: n, number; RM-ANOVA, repeated measures analysis of variance; GEE, generalized estimating equation; H2S, hydrogen sulfide.

Figure 1

(A) Partial pressure of oxygen and (B) carbon dioxide and (C) mean pulmonary artery and (D) airway pressures over time during reperfusion. Lungs pre-treated with room air are displayed with a dashed line. Lungs pre-treated with hydrogen sulfide are displayed with a solid line. Asterisks indicate a post hoc statistical difference at given time points as determined by the Tukey-Honest significance difference test. Abbreviations: n, number; RM-ANOVA, repeated measures analysis of variance; GEE, generalized estimating equation; H2S, hydrogen sulfide.

Figure 2

Reactive oxygen species levels stratified by treatment. Lungs pre-treated with room air are displayed with shaded bars. Lungs pre-treated with hydrogen sulfide are displayed with solid bars. Asterisks indicate a post hoc statistical difference at given time points as determined by the Tukey-Honest significance difference test. Abbreviations: n, number; RM-ANOVA, repeated measures analysis of variance; GEE, generalized estimating equation; RFU, relative fluorescence units; H2S, hydrogen sulfide.

Figure 3

Relative mitochondrial cytochrome c oxidase activity stratified by treatment. Lungs pre-treated with room air are displayed with shaded bars. Lungs pre-treated with hydrogen sulfide are displayed with solid bars. Asterisks indicate a post hoc statistical difference at given time points as determined by the Tukey-Honest significance difference test. Abbreviations: n, number; COX, cytochrome c oxidase; RM-ANOVA, repeated measures analysis of variance; AU, arbitrary units; H2S, hydrogen sulfide.

Figure 4

Cyclic GMP levels at the conclusion of reperfusion stratified by treatment. Lungs pre-treated with room air are displayed with shaded bars. Lungs pre-treated with hydrogen sulfide are displayed with solid bars. P-value determined by Student’s t-test. Abbreviations: n, number; GMP, guanosine monophosphate; H2S, hydrogen sulfide.